The present invention relates to a gasket, and more particularly to a gasket for use as a thin seal in fuel cells, secondary batteries, condensers, etc.
For gaskets used in fuel cells, secondary batteries, condensers, etc., rubber materials are widely used. Seal materials for these applications are much used for stacking a large number of cells one upon another, and the stacked products themselves, e.g. fuel cells, secondary batteries, condensers, etc. can be reduced in size by use of seal, materials as thin as or as narrow as possible.
As to thin seals for these applications, a gasket (JP-A-9-231987, JP-A-7-263004, JP-A-7-226220, JP-A-7-153480, etc.) and a gasket comprising a rubber sheet and a foamed sponge layer disposed thereon (JP-A-312223) have been proposed, but all of these thin seals are not directed to satisfying such requirements as reduction in thickness of seals, prevention of positional alignment failure during the assembling, reduction in specific pressure, specific pressure uniformalization, etc., and are hard to satisfy, if any, all these requirements.
That is, the ordinary separated type gaskets can satisfy only the reduction in specific pressure, specific pressure uniformalization, etc. but fails to satisfy reduction in thickness of seals, positional alignment failure during the assembling, etc. at the same time.
When the rubber hardness is high in case of stacking a large number of unit cells one upon another, tightening force of seal is liable to become uneven locally or depending on stacking positions, and thus a low rubber hardness is required for the rubber seal materials.
When the rubber seal materials are thin or narrow, or low in hardness, the seal materials themselves become so limp and soft, that it is difficult to mount the seals on the seal positions exactly and rapidly during the cell assembling and liable to cause a sealing failure in the stacked products.
To improve handling of seal materials, a somewhat hard and thin substrate, e.g. a stainless steel sheet (SUS grade), whose one side or both sides are integrally molded with a thin or narrow low-hardness rubber seal, is used, and such a substrate-integrated seal never undergoes considerable sagging when its one end is picked up and thus can be mounted on the desired position exactly, thereby facilitating the cell assembling work.
However, such integration of the substrate with rubber requires an additional adhesive to bond the substrate to the rubber, and thus an additional coating step and a drying step of the adhesive are required, resulting in a cost increase. Furthermore, components of the adhesive are partially extracted into the electrolytic solution, etc. with a risk of contamination of the electrolytic solution or catalysts.
Furthermore, from the viewpoints of performance or life of cells (including fuel cells and secondary batteries), condensers, etc., materials incapable of contaminating liquids to be used in the cells, etc. such as electrolytic solution, etc. or catalyst for promoting the reaction, etc. (e.g. a catalyst layer of platinum, etc. present on both sides of an electrolyte membrane or in the electrolyte membrane) are required as the materials for use in the cells or condensers.
Less harmful extractable components and no contamination are required for seal materials for use in the cells or condensers, so that the seal material components may not give no adverse effect at all on the cells or condensers, particularly in case of fuel cells, contamination, if any, of catalyst (Pt) with extracted components from cell member can decrease power generation performance, leading to risks such as a failure of stable power supply.
Furthermore, in case of fuel cells, the electrode plates, solid electrolyte membranes, separating plates, etc. are fastened by compression, and thus a smaller reaction force is require, during the fastening. In the fuel cells, it is necessary that the electrolyte membrane must be always wet and thus extractable components from the seal material into water supplied to keep the wet state or into water formed by reaction of hydrogen with oxygen (the electrolytic solution) must be less.
An object of the present invention is to provide an integrated gasket of a substrate (or a carrier member) and a rubber layer (or an elastomeric polymer member), which can be used as a thin seal capable of satisfying reduction in specific pressure and specific pressure uniformalization and also reduction in thickness of seal materials, positional alignment failure during the assembling, etc. at the same time, and also incapable of contaminating the electrolytic solution, catalyst, etc. in the cells or condensers, when set therein.
The object of the present invention can be attained by a film-integrated gasket, which comprises a resin film (or a carrier member) and rubber layer (or an elastomeric polymer member) having an adhesiveness to the resin film (adhesive rubber) by molding.
Another object of the present invention is to provide a static gasket having no contaminants contaminating the fluid to be sealed.
The object of the present invention can be can be attained by a static gasket for sealing fluids, comprising a carrier member (or a substrate) and an elastomeric polymer member (or a rubber layer) having an adhesive component which bonds to said carrier member and prevents contamination of the fluids to be sealed. Namely, the elastomeric polymer member has an adhesive component in itself which has a property to bond to the carrier member and has substantially no contaminants contaminating the sealing fluids to be sealed. Between the carrier member and the elastomeric polymer member there is no additional adhesives which could cause contamination of the sealing fluids to be sealed.
Still another object of the present invention is to provide a static gasket the deformation or compression of which is limited to a specific level when in use.
Said still another object of the present invention can be attained by a static gasket comprising a resin film or a carrier member, an elastomeric polymer member disposed on said carrier member and a compression limiter placed adjacent to the elastomeric polymer member for limiting the distance between fastening plates the gasket is placed therebetween.
According to the invention the distance between the fastening plates is limited so that the deformation or compression of the gasket can be limited or controlled arbitrarily by changing the thickness of the limiter.
Any resin film can be used as a substrate or a carrier member, so long as it can withstand the molding temperature of the adhesive rubber (about 100xc2x0 C.xcx9cabout 200xc2x0 C.). For example, polyester film (typically polyethylene terephthalate), polyimide film, polyamideimide film, etc. can be used. From the viewpoint of heat resistance, polyimide film is preferable. From the viewpoint of producing a thin seal, the resin film must have a thickness of about 10xcx9cabout 500 xcexcm, preferably about 50xcx9cabout 10 xcexcm.
Any rubber or elastomeric polymer member having an adhesiveness toward the resin film can be used, so far as the rubber can form a rubber layer of low hardness (JIS A hardness: about 70 or less, preferably about 10xcx9cabout 40). For example, silicone rubber, fluorosilicone rubber, fluoro rubber, nitrile rubber, EPDM, etc. each in a liquid or paste state can be used. The low hardness of the rubber can decrease the reaction force generated when the electrode plates, solid electrolyte membranes, separate plates, etc. are fastened together by compression in case of, e.g. fuel cells.
Among these adhesive rubbers, silicon rubber in a liquid or paste state, particularly addition reaction-curable type silicone rubber is preferable. Addition reaction-curable type silicone rubber comprises a composition comprising (a) 100 parts by weight of alkenyl group-containing organopolysiloxane and (b) such an amount of organohydrogenpolysiloxane having at least 2H atoms directly bonded to the Si atom in one molecule as to make 0.4-5.0 parts of the H atom (i.e., SiH group) to one part of the alkenyl group of the component (a), and practically, commercially available products, e.g. X-34-1277, X-34-1547, X-34-1427, X-34-1464, X-34-1535, X-34-1534, etc. (products made by Shin-Etsu Chemical Co., Ltd. Japan) can be used as such.
The composition containing (a) and (b) components further contains a catalytic amount of Pt, etc. and (c) about 0.1-about 50 parts by weight of an adhesiveness-endowing component, thereby forming the addition reaction-curable type silicone rubber. Furthermore, not more than about 50 parts by weight of fine silica powder having a specific surface area of not less than about 50 m2/g may be added thereto.
Alkenyl group-containing organopolysiloxane as component (a) and organohydrogenpolysiloxane as component (b) undergo cross-linking reaction in the presence of a Pt catalyst by adding hydrogen atoms to the alkenyl groups as follows: 
Adhesiveness-endowing agent to be added to the foregoing components (a) and (b) as component (c) includes, for example, organosilicone compounds having at least one H atom directly bonded to the Si atom (SiH group) in one molecule, as given below: 
Integration of the resin film with the addition reaction-curable type silicone rubber layer (silicone rubber in a liquid or paste state) comprising the foregoing components by molding can be carried out by a procedure of placing uncured liquid or paste silicone rubber in a desired pattern onto a premolded resin film, followed by heating below the softening point of the film-constituting resin (mold process, coating process, dipping process, etc.), a procedure of placing uncured liquid or paste silicone rubber onto a premolded resin film, followed by compression with heating below the softening point of the film-constituting resin, a procedure of premolding a film in a mold by a molding machine and injecting liquid or paste silicone rubber under a low injection pressure into the mold, followed by heating at the molding temperature of the silicone rubber, etc.
Rubber layer or an elastomeric polymer member, which is characterized as a self-bonding elastomer member having a property to bond to the resin film directly, is molded on one side or both sides of the resin film or a carrier member to thickness of about 0.1xcx9cabout 10 mm, preferably about 0.5xcx9cabout 2 mm on one side of the resin film. It is particularly preferable to mold the rubber layer in an inverted T-type stepped wall cross-section with a layer bottom width of about 0.5xcx9cabout 5 mm, preferably about 1xcx9cabout 2 mm (as shown by reference numerals 8 and 9 in FIG. 1), because the reaction force is lowered when the fuel cell members are fastened by compression.